The objective of this research is to study the functional interrelationships between the plasma membrane and the cytoplasmic membranes of rat liver. To this end, the enzyme 5'-nucleotidase will be purified, and the lipid and carbohydrate content of the protein determined. The mechanism by which the concentration of the enzyme in individual organelles is determined will be investigated by analysing the possible association of the enzyme with other membrane proteins. The effect of lipids on the activity of the enzyme will be studied by determining the effect of individual phospholipids on the stability of the enzyme and on transitions in the energy of activation. By following the labelling kinetics of the pure protein, it is hoped to determine the sites of synthesis and breakdown of the enzyme. Finally, cytochemical procedures will be employed to investigate the mechanism by which the orientation of the enzyme in membranes is controlled.